Process for removing acidic sulfur compounds from hydrocarbon distillates



Patented Aug. 17, 1948 UNITED STATES PATENT OFFICE PROCESS FOR REMOVINGACIDIC SULFUR COMPOUNDS FROM HYDROCARBON DIS- TILLATES Donald 0. Bond,Northbrook, and Nelson B.

Russell, Winnetka, 11]., assignors to The Pure Oil Company, Chicago,111., a. corporation of This invention relates to a method for removingacidic sulfur compounds from water-immiscible fluids and is moreparticularly concerned with regeneration of alkaline reagents which havebeen employed to remove mercaptans from petroleum oils.

It is now common practice to extract mercaptans and other acidic sulfurcompounds from hydrocarbon fluids, particularly gasoline and similarlight oil distillates, by treatment of the distillate with aqueousalkali solution containing solubility promoters. One process forextracting mercaptans from petroleum distillates is the Mercapsolprocess in which an aqueous sodium hydroxide solution, containing alkalimetal naphthenates together with cresols as solubility promoters, isused. The Mercapsol process and the reagent used therein are disclosedin Patent No. 2,297,621. Other solubility promoters which are incommercial use are the alkali metal salts of low boiling fatty acids,particularly isobutyric acid.

Aqueous alkali solutions of the type just described, after they have:been used to extract mercaptans from petroleum distillates, areordinarily regenerated for re-use by steam stripping at temperatures ofthe order of ZOO-300 F. Steam stripping hydrolyzes the mercaptides,thereby releasing mercaptans which pass overhead with the steam. Whilethis method of regeneration has proved satisfactory, the cost of thesteam required for the stripping operation is relatively high.

It is an object of this invention to provide a process for removingacidic sulfur compound from hydrocarbon fluids.

It is another object of this invention to provide an improved method ofregenerating alkali solutions which have been used for removing acidicsulfur compounds from hydrocarbon fluids.

It is still a further object of the invention to provide a method forregenerating used alkali solutions by means of oxygen oroxygen-containing gas.

Still another object of the invention is to provide a catalyst capableof accelerating regeneration of used alkali solutions by means of airblowing.

Other objects and advantages will be apparent from the followingdescription of the invention.

It has now been found that regeneration of alkaline solutions which havebeen used for removing acidic sulfur compounds from water-immisciblefluids such as petroleum oils may be greatl accelerated by contactingthe solutions with free oxygen-bearing gas, such as air, in the presenceof a small amount of 3,4 dihydroxy diphenyl and/or 2,5 dihydroxydiphenyl or mixtures of the two.

In accordance with the invention the hydrocarbon fluids from which it isdesired to extract merca-ptans or other acidic sulfur compounds arecontacted with aqueous alkali solution such as aqueous sodium orpotassium hydroxide containing from about 5 to 30% by weight of freealkali metal hydroxide, with or without solubility promoters, in a ratioof approximately 5 to 50% by volume of alkali solution per volum ofliquid undergoing treatment. The used alkali solution is then contactedwith air preferably countercurrently in a packed tower in the presenceof 3,4 and/or 2,5 dihydroxy diphenyl in an amount of from approximately.05 to 3 percent by weight of the alkali solution. The used alkali iscontacted with a sufficient amount of air and for a suflicient length oftime to reduce the mercaptan content to a point suitable for re-use ofthe solution in further extraction of mercap'tans and/or other acidicsulfur compounds. The regeneration is preferably not carried tocompletion since the catalyst may be destroyed if all the mercaptan orother acidic sulfur vcompound is removed from the alkali solutionundergoing regeneration thereby necessitating the replacement of thecatalyst for the succeeding regeneration step. Ordinarily we do notreduce the mercaptan sulfur content of the used alkali duringregeneration below 0.2 to 0.6% by weight.

The air regeneration may be conducted at ordinary atmospherictemperatures. Temperatures between and F. are satisfactory. Lower orhigher temperatures may be used. However, lower temperatures requirelonger periods for regeneration whereas higher temperatures are notdesirable because of the possibility of forming undesirable oxidationby-products.

In order to demonstrate the efficacy of 3,4 and 2,5 dihydroxy diphenyl,a number of individual compounds and substances were tested in thefollowing manner: 1.86 cubic centimeters of normal butyl mercaptan weredissolved in 50 cubic centimeters of an aqueous sodium hydroxidesolution containing 10% by weight of sodium hydroxide in order to give asolution containing 1% by weight of mercaptan sulfur. To the sodiumhydroxide solution was added 0.55 gram of the desired catalyst in orderto have present 1% by weight of catalyst in the solution. In some casesin order to hasten solution of the catalyst, the solution was agitatedwith nitrogen which had 3 first been passed through alkaline pyrogallolsolution to remove any oxygen. In some cases the entire amount ofcatalyst did not dissolve in the alkali solution. The solutioncontaining the sodium hydroxide, normal butyl. mercaptan and catalystwas placed in a 100 cc. graduated cylinder filled to the 75 cc. markwith No. 4 glass.

beads. Air was bubbled through the solution for 1 hour at the rate of0.03'cu'bic foot per'hour' by means of a tube reaching to the bottom ofthe cylinder. After the solution had been blown for 1 hour with air atroom temperature (ap-J proximately 75 F.) it was-extractedwitheapproximately 100 cubic centimeters of V. M'. P. 1

naphtha to remove the disulfides that had formed.

The resulting naphtha containing. the disulfides was treated with acidicsilver nitrate to remove. any unoxidized mercaptans and the solution wasAmong the'com:

then analyzed for disulfides. pounds tested were 3,4 dihydroxy diphenyl,2,5 dihydroxy diphenyl, -4,4 dihydroxydiphenyl, o-hydroxy diphenyl andp-hydroxy diphenyl. The results of these tests are tabulated in thefollowing table. 1

- Table uur oun .on-uy Cataly st Used in Test in Naphtha M emaptanSolution Oxidized 3,4 Diliydroxy Diphenyl 0.125 22. 6 2,5 Dihydroxydiphenyl I 0.125 22.6 None 0.005 0.9 4,4 Dlhydroxy diphenyl 0.005 0. 9o-Hydroxy diphenyl 0. 004 0.7 p-Hydroxy diphenyl I 0.003 0.5

1 Catalyst did not entirely dissolve.

stored to a condition .suitablcfor reuse. The.

amount of 3,4 and/r. 2,5 dihydroxy diphenyladded to the alkali willdepend on the particular catalyst andto some extent upon particularregeneration conditions employed, but is ordinarily from about 0.1 to 2%by weight. The alkali solution may be repeatedly regenerated although itmay be necessari to add additional catalyst from 4 time to time to makeup for any loss and maintain the desired eificiency.

It is to be understood that the rate of air blowing used in the specificexamples herein disclosed is not .to be considered as the most desirablerate for commercial operation. Obviously where large scale equipment isused the rate of airblowing will considerably exceed that used inthe'tests;;.The rate of air blowing may vary with- 10 iri'wide limitsand will be adjusted in accordance with the size and type of equipmentused in the regeneration step to obtain most rapid regeneration withminimum loss of solution by carry-over in the exhaust air.

It is claimed: 1. {Iheprocess of regenerating aqueous alkali solution'used to extract acidic sulfur compounds from hydrocarbon fluidscomprising contacting said solution with free-oxygen containing gas inthe presence of a modicum of a hydroxy aromaticcompound selected from.the group consisting of 3,4 dihydroxy diphenyl and 2,5 d-i'hydroxydiphenyl. 4

2. Process in accordance with claim 1 in which the vhydroxy aromaticcompound is present in an efi'ective amount between .01 and 2% by weightof the alkali solution.

3. .Process in accordance with claim 1 in which the hydroxy aromaticcompound is 3,4 dihydroxy 3 diphenyl.

4. Process in accordance with claim 1 in which the hydroxy aromaticcompound is 2,5 dihydroxy diphenyl.

5. The method of regenerating aqueous caustic alkali solution which hasbeen used to extract mercaptan from petroleum distillates, comprisingcontacting .said solution, containing an amount between about 0.1 and 2%by weight suificient to function as an oxidation accelerator of ahydroxy aromatic compound selected from the group consisting of 3,4dihydroxy diphenyl and 2,5 dihydroxy diphenyl, with air until asufficient amount of the sulfur compounds have been converted todisulfides to make the alkali solu- 545 tion efiective for further usein extracting mer- DONALD C. BOND. NELSON B. RUSSELL.

